Sheet curl control apparatus

Abstract

The invention relates to a sheet curl control apparatus including a decurler (350) for reducing the curl in sheet material passing therethrough and adjusting means coupled to the decurler (350) for adjusting the decurling action of the decurler (350). Sensing means (406) in the form of an infra-red emitter (408) and two infra-red detectors (410 and 412) are employed for sensing the extent of any residual curl left in the sheet material after it has passed through the decurler (350), and for feeding a signal indicative of the residual curl to control means, conveniently including a stepper motor, for automatically adjusting the adjusting means, for example a rack and pinion arrangement, thereby to alter the decurling action of the decurler (350) in a predetermined manner. The sheet curl control apparatus is described in relation to its use in a copier for duplex copying.

I claim: 
     
       1. A sheet curl control apparatus including a decurler for reducing the curl in sheet material passing therethrough and adjusting means coupled to the decurler for adjusting the decurling action of the decurler, characterized by sensing means for sensing the extent of any residual curl left in the sheet material after it has passed through the decurler, and for feeding a signal indicative of the residual curl to control means for automatically adjusting said adjusting means thereby to alter the decurling action of the decurler in a predetermined manner, and wherein said sensing means comprises a radiation source and two radiation detectors for detecting radiation emitted by said radiation source, said radiation detectors being spaced apart and arranged such that movement of the sheet material along the sheet path downstream of said decurler causes the light beams reaching the detectors to be interrupted in succession by the feed edge of the sheet material, the time interval between interruption of the light beams at the two detectors being a function of the extent of residual curl in the sheet material. 
     
     
       2. The sheet curl apparatus as claimed in claim 1, wherein said sensing means is located adjacent a straight section of sheet path downstream of said decurler. 
     
     
       3. The sheet curl apparatus as claimed in claim 2, wherein said sensing means is located adjacent a horizontal section of sheet path downstream of said decurler. 
     
     
       4. The sheet curl apparatus as claimed in claim 1, wherein said radiation source is located on one side of said straight section of sheet path downstream of said decurler and the detectors are spaced apart on the opposite side of the sheet path. 
     
     
       5. The sheet curl apparatus as claimed in claim 4, wherein said radiation source is positioned above the sheet path and the detectors are positioned below the sheet path, the time interval between interruption of light at the detectors being inversely proportional to the sheet curl. 
     
     
       6. The sheet curl apparatus as claimed in claim 5, wherein said radiation source is an infra-red emitter and said detectors are each infra-red sensors. 
     
     
       7. The sheet curl apparatus as claimed in claim 6, wherein said control means includes a motor with a drive shaft operable in response to a feedback signal from said sensing means to adjust said adjusting means. 
     
     
       8. The sheet curl apparatus as claimed in claim 7, wherein said adjusting means is a rack and pinion arrangement, said rack being mounted to a baffle of said decurler and said pinion being driven by a mechanical coupling arrangement to said drive shaft of said motor. 
     
     
       9. The sheet curl apparatus as claimed in claim 8, wherein said motor is a stepping motor. 
     
     
       10. A copier defining therein a sheet path having a sheet curl control apparatus arranged therealong including a decurler for reducing the curl in sheet material passing through the decurler, lead-in guide means for guiding the sheet material into the decurler and adjusting means coupled to the decurler for adjusting the decurling action of the decurler, characterized in that said sheet curl control apparatus includes sensing means for sensing the extent of any residual curl left in the sheet material after it has passed through said decurler, and for feeding a signal indicative of the residual curl to control means for automatically adjusting said adjusting means thereby to alter the decurling action of the decurler in a predetermined manner, and wherein said sensing means comprises a radiation source and two radiation detectors for detecting radiation emitted by said radiation source, said radiation detectors being spaced apart and arranged such that movement of the sheet material along the sheet path downstream of said decurler causes the light beams reaching the detectors to be interrupted in succession by the feed edge of the sheet material, the time interval between interruption of the light beams at the two detectors being a function of the extent of residual curl in the sheet material. 
     
     
       11. A copier for duplex copying including a photoreceptor, a copy sheet tray, a duplex buffer tray, sheet feeders associated with said trays for feeding sheets from said trays to the photoreceptor, a fuser for fixing images received on said sheets at the photoreceptor, a sheet return path for conveying simplex sheets which have received an image on one side at the photoreceptor to said duplex buffer tray from said fuser for refeeding to the photoreceptor to receive a second image on the other side and a sheet curl control apparatus in the sheet return path, characterized in that said sheet curl control apparatus includes sensing means for sensing the extent of any residual curl left in the sheet material after it has passed through a decurler, and for feeding a signal indicative of the residual curl to control means for automatically adjusting said adjusting means thereby to alter the decurling action of said decurler in a predetermined manner, and wherein said sensing means comprises a radiation source and two radiation detectors for detecting radiation emitted by said radiation source, said radiation detectors being spaced apart and arranged such that movement of the sheet material along the sheet path downstream of said decurler causes the light beams reaching the detectors to be interrupted in succession by the feed edge of the sheet material, the time interval between interruption of the light beams at the two detectors being a function of the extent of residual curl in the sheet material.